Along with recent progress in semiconductor technology, it has been attempted to realize a very small micro machine using semiconductor manufacturing technology, and actuators and other electromechanical elements have been developed. By using such elements, mechanical parts of small size and high precision can be realized, and the productivity can be dramatically improved by employing a semiconductor process. In particular, actuators employing piezoelectric elements are used for fine displacement of a scanning tunneling microscope and for fine positioning of a head slider of a magnetic recording and reproducing disk device (hereinafter called disk device).
For use in a disk device, for example, a piggyback actuator is developed as an actuator for positioning the magnetic head for recording at higher density (for example, Ultrahigh TPI and piggyback actuator, IDEMA Japan News No. 32, pp. 4–7, International Disk Drive Association; and Japanese Laid-open Patent Publication No. 2002-134807). In these examples, a magnetic head for recording and reproducing information on a magnetic disk is formed on a head slider, and the head slider is fitted to a flexure. This flexure is fitted to a suspension, and the suspension is fixed to an arm. In this configuration, the arm is oscillated by a voice coil motor (hereinafter called VCM), and the magnetic head is positioned on a predetermined track position on the disk, and moreover fine positioning is possible by using an actuator composed of a piezoelectric element.
FIG. 22 is a plan view of an example of a conventional piggyback actuator used in a disk device. FIG. 22 shows only the actuator region for fine positioning using a thin film piezoelectric element fitted to a flexure. FIG. 23 is a sectional view along line 23—23 of in FIG. 22. A thin film piezoelectric element 100 is composed of a pair of a first piezoelectric element unit 100A and a second piezoelectric element unit 100B. They are mirror symmetrical to each other, and adhered and fixed on a flexure 122. One end of the flexure 122 is affixed to a suspension 140. One end of the suspension 140 is affixed to an arm (not shown).
One of the first piezoelectric element unit 100A and second piezoelectric element unit 100B is displaced in a direction extending as indicated by arrow E, and the other is displaced in a direction contracting as indicated by arrow D, so that a slider holder 160 provided at the leading end is rotated finely. As a result, a head slider 101 fitted to the slider holder 160 is rotated finely, and a magnetic head 130 fitted to the leading end of the head slider 101 is moved finely as indicated by arrow C.
As shown in FIG. 23, the first piezoelectric element unit 100A and second piezoelectric element unit 100B each have a two-layer laminated structure of a first piezoelectric thin film 111A and second piezoelectric thin film 111B. The first piezoelectric thin film 111A is enclosed by a first electrode 112B and a second electrode 112A. Similarly, the second piezoelectric thin film 111B is enclosed by a third electrode 112C and fourth electrode 112D. The second electrode 112B and third electrode 112C are adhered by way of an adhesive layer 113, so that the entire structure is integrally fixed.
At the end of the first piezoelectric element unit 100A and second piezoelectric element unit 100B, via holes 114, 115 and wiring connections 116, 117 are provided for forming electrode terminals. The via holes 114, 115 are used for forming the wiring connections 116, 117 for short-circuiting the second electrode 112B and third electrode 112C. A terminal wire 118 is connected to the wiring connections 116, 117, and this terminal wire 118 is connected to a grounding electrode 119.
On the other hand, a terminal wire 120 is connected to the first electrode 112A and fourth electrode 112D of the first piezoelectric element unit 100A, and this terminal wire 120 is connected to a driving power source 121A. Thus, a specified voltage can be applied to the first piezoelectric element unit 100A. A terminal wire 120 is connected to the first electrode 112A and fourth electrode 112D of the second piezoelectric element unit 100B, and this terminal wire 120 is connected to a driving power source 121B. Thus, a specified voltage can be applied to the second piezoelectric element unit 100B.
The first piezoelectric element unit 100A and second piezoelectric element unit 100B are adhered and fixed on a flexure 122.
To realize such actuator for fine positioning, it is important to develop a thin film piezoelectric element small in size, light in weight, and large in displacement at low voltage. However, the thin film piezoelectric element is complicated to manufacture and is relatively expensive. It is hence demanded to decrease the number of wirings of the thin film piezoelectric element, facilitate the assembling, and simplify the manufacturing process.
In the prior art, however, such demand could not be satisfied. That is, as the wiring for the thin film piezoelectric element 100, connection from the first piezoelectric element unit 100A and second piezoelectric element unit 100B to the grounding electrode 119 as a common electrode is necessary, and the number of wirings on the flexure 122 increases. For this purpose, connection parts are needed, and it was difficult to simplify the process. In the first piezoelectric element unit 100A and second piezoelectric element unit 100B, the process for forming the via holes 114, 115 and wiring connections 116, 117 is needed, which lowered not only the manufacturing yield but also the reliability as the actuator.
An actuator in a laminated structure of piezoelectric thin film is disclosed, for example, in Japanese Laid-open Patent No. H8-88419. In this example, on a single crystal substrate of magnesium oxide (MgO), strontium titanate (SrTiO3) or sapphire (Al2O3), an electrode layer of platinum (Pt), aluminum (Al), gold (Au), or silver (Ag) is formed, together with a piezoelectric layer made of piezoelectric material such as lead zirconate titanate (PZT) or lead lanthanum zirconate titanate (PLZT), and an electrode layer of similar material, and a junction layer composed of glass or silicon is formed on these films, and thereby a piezoelectric member is fabricated. By repeating the process of mutually bonding piezoelectric members by way of a junction layer by anodic bonding, the process of forming a junction layer on an electrode layer exposed by removing the substrate at the laminating side by polishing, and the process of bonding this bonded layer and a bonded layer of another piezoelectric member in the same procedure and removing the substrate again, a laminated body laminated in plural layers is formed. Finally, by taking out the inner layer electrodes in the laminated body mutually from both sides, a laminated actuator is realized. In this manufacturing method, the substrate is removed by etching process after polishing so that residual portion may not be formed, and as the mutual bonding method of piezoelectric members, not limited to anodic bonding, surface activated bonding and adhesive bonding are also disclosed.
In this disclosed example, however, an external electrode is formed from two sides of a laminated body of multiple layers of piezoelectric members by way of an insulating layer, and at least this external electrode must be formed on each one of the laminated bodies, and mass productivity is not satisfied. In this configuration, yet, since a displacement is caused in the direction perpendicular to the substrate surface, it is not suited to a structure used, for example, as an actuator for fine positioning of a head slider of a disk device.